This invention relates to the treatment of cooking oils and fats. More particularly, this invention relates to the treatment of cooking oils and fats to reduce the free fatty acid content thereof by contacting the cooking oils or fats with magnesium silicate and alkali materials such as calcium hydroxide.
Cooking oils and fats are employed in general for the cooking or frying of foods such as chicken, fish, potatoes, potato chips, vegetables, and pies. Such frying may take place in a restaurant wherein food is prepared for immediate consumption, or in an industrial frying operation where food is prepared in mass quantities for packaging, shipping, and future consumption.
In a typical restaurant frying operation, large quantities of edible cooking oils or fats are heated in vats to temperatures of from about 315.degree. F. to about 400.degree. F. or more, and the food is immersed in the oil or fat for cooking. During repeated use of the cooking oil or fat, the high cooking temperatures, in combination with water from the food being fried, cause the formation of free fatty acids (or FFA). An increase in the FFA decreases the oil's smoke point and results in increasing smoke as the oil ages.
Industrial frying operations involve the frying of large amounts of food for delayed consumption. Often, this is a continuous operation with the food being carried through the hot oil via a conveyor.
Industrial fryers of meat and poultry must follow the guidelines of the FDA Food Safety and Inspection Service (FSIS) Meat and Poultry Inspection Manual. The following are excerpts from that manual:
Section 18.40 Frying (a) Meat
Length of time fats and oils may be used for deep fat frying varies with temperature, quality of new fat added daily, and fat treatment during use. Suitability of these fats for further use can be determined from degree of foaming during use or from color, odor, and flavor.
Fat or oil should be discarded when it foams over the vessel's side during cooking, or when its color becomes almost black as viewed through a colorless glass container.
Section 18.40 Frying (b) Poultry (5) Fat Acceptability
Used fat may be made satisfactory by filtering, adding fresh fat, and cleaning the equipment regularly.
Large amounts of sediment and free fatty acid content in excess of 2 percent are usual indications that frying fats are unwholesome and require reconditioning or replacement.
Most industrial fryers use the 2% free fatty acid (FFA) limit, or less if mandated by their customers, for poultry as their main specification for oil quality, regardless of the food being fried.
In addition to hydrolysis, which forms free fatty acids, there occurs oxidative degeneration of fats which results from contact of air with hot oil, thereby producing oxidized fatty acids (or OFA). Heating transforms the oxidized fatty acids into secondary and tertiary by-products which may cause off-flavors and off-odors in the oil and fried food.
Caramelization also occurs during the use of oil over a period of time, resulting in a very dark color of the oil which, combined with other by-products, produces dark and unappealing fried foods.
Because of the cost resulting from the replacing of the cooking oils and fats after the use thereof, the food industries have searched for effective and economical ways to slow degradation of fats and oils in order to extend their usable life.
U.S. Pat. No. 4,112,129, issued to Duensing, et al., discloses a composition comprised of diatomite, synthetic calcium silicate hydrate, and synthetic magnesium silicate hydrate may be employed for reclaiming used fats and oils.
U.S. Pat. No. 4,681,768, issued to Mulflur, et al., discloses a process for treating used cooking oil or fat by contacting used cooking oil or fat with a high surface area amorphous synthetic magnesium silicate having a surface area of at least 300 square meters per gram.
Most industrial fryers use Silasorb (Celite Corporation, Denver, Colo.) which is a synthetic calcium silicate, as their filter medium because it is very effective in lowering free fatty acid concentration. Silasorb lowers the free fatty acid (FFA) concentration of the oil by a combination of adsorption and neutralization. The use of Silasorb, however, often darkens the oil.
In addition, the product of the neutralization of a fatty acid with an alkaline metal is a fatty acid soap. The amount of soap formed is dependent on the amount of alkaline metal present, and the initial percentage of free fatty acids in the oil. When the soap level is high, the oil foams. The use of Silasorb in order to lower the free fatty acid concentration sometimes results in uncontrollable foaming.